The invention relates to a locking device with a cylinder lock and a flat key wherein the cylinder lock comprises a rotor rotatable in a stator with a key channel, and guides disposed approximately at right angles to the longitudinal axis of the rotor and parallel to the broad sides of the key channel which {guides} comprise tumblers provided with carriers projecting into the key channel, and the flat key comprises on the broad sides guide tracks which when the key is introduced into the key channel engage the carriers of the tumblers and at least in one portion of the tumblers on the rear side facing away from the key channel a hollow is disposed which cooperates with an additional blocking element.
Such a locking device with a cylinder lock and a flat key is known from U.S. Pat. No. 3,035,433. In the rotor of a cylinder lock is disposed a key channel which extends in the direction of the lock, respectively rotor, axis. This key channel serves for receiving a flat key. On the broad sides of the flat key are disposed guide tracks for positioning tumblers in the cylinder lock. These tumblers are supported in the lock in guides which are at right angles to the lock axis and extend parallel to the broad sides of the key channel. The tumblers comprise carriers which project into the key channel, respectively protrude into it and when the key is introduced into the key channel engage the guide tracks on the key. When the key is introduced completely into the key channel, and provided the guide tracks have the correct positioning planes for the carriers, the tumblers are completely in the rotor of the lock, and the rotor can be rotated in the stator. The lock comprises also an additional blocking element. This is disposed between the rear side of the tumblers and the stator and comprises a blocking bar which extends parallel to the lock axis and over all tumblers. This blocking bar is pressed by springs toward the outside into a groove with ramp surfaces in the stator. It is displaced from the groove in the stator by rotating the rotor and pushed against the rear side of the tumblers. In order for this displacement to be possible, into the rear side, facing away from the key channel, of the tumblers one groove each is worked which extends parallel to the blocking bar. The depth of this groove corresponds at least to the displacement path of the blocking bar during the rotation of the rotor. Otherwise, the rotor cannot be rotated and the lock cannot be opened.
Blocking bars of the known type form an additional element which secures the rotor in the stator against rotational movements. However, they do not form an additional security against unauthorized manipulations, for the example the so-called picking of the lock since the tumblers can be brought independently of the blocking bars into the opening positions. During the positioning process of the tumblers no cooperation exists between tumblers and blocking bar. Cooperation is only initiated if first the rotor can be rotated in the stator, i.e. if the tumblers are correctly positioned. As soon as the tumblers are in the correct opening position, however, the displacement path for the blocking bars is also released, since the groove on the rear side of the tumbler is also in the correct position.